A currently preferred method for collating fine wire staple sticks is to use a liquid adhesive system that is applied to a multi-end band wire. The adhesive is then dried by heat and air leaving a solid film coating on the band of wire for pressing staple sticks in line or wound up onto spools for subsequent staple pressing.
These liquid adhesive systems must dry quickly to produce a high strength film to hold the strips of the band together through wind up. The adhesive must also have sufficient tensile strength and impact resistance to pass the pressing step and ultimate end use, discharge from a fastening gun.
Additional problems with the liquid systems include the use of solvents that are regulated requiring special handling equipment, process equipment and disposal equipment. For some liquid adhesive systems, expensive drying equipment must be used utilizing high energy to remove up to 80% by weight of the supplied liquid adhesive system.
More efficient, lower cost drying systems have been designed and utilized through the years with significant improvement but the use of solvents and their associated costs have not changed.
Wire end machines have utilized thermally activated film tapes which are applied after the staples have been pressed. These tapes, however, are not designed to cover the total surface of the staple stick and can only be applied to the outer surface limiting stiffness and impact resistance. This production method is primarily used for lower volume specialty staples where high speed volume is not critical.
It would desirable to have thermally activated adhesive films which can set quickly and can have consistent physical properties, such as tensile strength, impact resistance, and high adhesion to metal surfaces.
Broadly the invention comprises a 100% solid thermally activated adhesive film, instead of a liquid adhesive, to coat and hold together a multi-strip band of wire together through a high volume, high speed banding line. Heat is used for film activation. The adhesive film reduces the amount of energy needed to process staples, reduces capital equipment needs and also offers an alternative adhesive system for improved physical properties, e.g. tensile strength, impact resistance and adhesion.
In the preferred embodiment, the adhesive system comprises a three-part, polyethylene based polymer. The modified polyethylene is 100% solids, activates in a temperature range of 200° F. to 450° F., is acid modified for polarity sites for bonding, and embodies a rubber polymer or elastomeric phase to minimize adhesive surface fracture and ensures high adhesion to the metal surface.